Promotion of the lower limit of detection of gamma emitting nuclides in radioaerosol samples after Fukushima accident

摘要

Through placement in a few hours after collecting radioaerosol samples (in Shanghai) after Fukushima nuclear power plant (NPP) accident, radionuclides with gamma-emitting rays can be found to be nuclides (~(132)I/~(132)Te, ~(~129)I/~(1~29)Te) other than ~(131)I, ~134,137Cs because of the decrease in background baseline after the daughter 214 214 nuclides (i.e. ~(214)Bi, ~(214)Pb and etc.) of radon makes decay sharply. Based on aerosol sample collected by passing through 1,300 M~3 air in 24 h, the lower limit of detection (LLD) of ~(132)I/~(132)Te, ~(129)I/~(129)Te can be decreased from 6.11 x 10~(-5), 3.46 x 10~(-4)Bqm~(-3) after half an hour sampling to 1.64 x 10~(-5), 8.19 x 10~(-5) Bq m~(-3) after sampling 48 h sampling. Similarly, LLD can be decreased from 9.63 x 10~(-5) to 1.41 x 10~(-5) Bq m~(-3) for ~(131)I, 7.72 x 10~(-5) to 9.96 x 10~(-6) Bq m~(-3) for ~(134)Cs and 9.67 x 10~(-5) to 1.45 x 10~-5 Bq m~-3 for ~(137)Cs after the same time sampling. In the same time, the activities of daughter nuclides such as ~(214)Pb and ~(212)Bi from the decay of their parent nuclides ~(222)Rn and ~(220)Rn can sharply decrease from 2.45 x 10~(-2), 2.57 x 10~(-2) Bq m~(-3) to be ~ 10~(-4) Bq m~(-3) while the activities of the concerned nuclides ~(132)I/~(132)Te, 129 131 134137 ~(129)Te, ~(131)I, ~(134,137)Cs were almost constant. As our knowledge, it is the first time to report such case which is very helpful to monitor the leaked nuclides from NPP by aerosol sampling in both normal operation case and emergency case.